Intercropping Pea With Oilseeds Under Irrigation

Reason for the Study

Intercropping peas and canola is a common practice for some pea growers in Saskatchewan. This study examined the potential for this practice under irrigation.

Methods Used in the Experiments

The three-year experiment was carried out from 1991 to 1993. Radley (short, early, semi-leafless), Express (short, early) and Victoria (tall) varieties of pea were planted alone, and were intercropped with three oilseeds. Cutlass oriental mustard, Crusher and Global canola were the intercropped oilseeds. They were also sown alone for comparison.

Canola and mustard were sown at 10 kg/ha (9 lb/ac) at 2 cm (1/2 inch) depth using a drill with 20 cm (6 inch) row spacing. Peas were sown at 5 cm (2 inches) depth at 130 to 200 kg/ha (115 to 175 lb/ac), depending on seed size, using the same drill. When a mixture was planted, the oilseed and pea were planted in alternate rows at half the normal rate..

The oilseed planted alone received a normal rate of nitrogen in all years. In 1991, the intercrop mixes received a half rate of nitrogen. Soil nitrogen levels in 1992 and 1993 were high and no nitrogen was applied to the peas or to the mixes in those years..

Results

Total yields of the intercrop combinations were greater than for peas alone for all three pea varieties (Figure 1). Radley pea intersown with Cutlass mustard produced the greatest total yield..

Radley was the highest yielding pea when grown alone. Although it yielded less when intercropped than when sown alone, it was the highest yielding pea in any intercrop combination. Victoria, the tallest variety, yielded more when cropped with the oilseeds. Express yielded more when grown with mustard than when planted alone. There was no increase in yield of Express when cropped with Global..

Pea plant type had an effect on the results of intercropping. Yields of intercropped oilseeds were greatest when sown with the semi-leafless Radley pea and least when sown with the long-vined Victoria pea. The more competitive the pea, the lower the oilseed yield. If the pea variety is highly susceptible to lodging, it will yield more if intercropped with an oilseed than if sown alone..

All pea varieties produced larger seeds when grown with Cutlass than with canola or in pure stands (Figure 2). It is likely that the mustard held the peas in a more upright position which allowed better grain filling. The increased seed size appears to be partly responsible for the increased yield of Express and Victoria peas in the intercrop mixtures.

A further benefit of intercropping was evident in 1992. The pea plots lodged severely which created ideal conditions for development of Sclerotinia stem rot. Plots with peas only were heavily diseased. In contrast, peas held up by the intercrop oilseed were largely unaffected.

Economics of Intercropping

Table 1 summarized the yields of intercropped pea and oilseed averaged over the three years of the test. These averages are used to assess the economics of intercropping.

Figure 3 illustrates the gross return for Radley pea intercropped with Global canola compared to growing peas alone. Radley and Global are used in the comparison because the average yield of the mix was similar to that of Radley alone (Table 1), and because canola is more commonly grown under irrigation than is mustard..

When the oilseed price is relatively high compared to the pea price, there is an economic benefit to intercropping an oilseed with the pea crop. The gain in this test was greatest for a semi-leafless pea (Radley) grown with mustard. Similar results could be expected if a canola variety with the same standability as Cutlass mustard were used..

Results of the Study:

• Intercropping the semi-leafless pea variety, Radley, with Cutlass oriental mustard produced higher total seed yield than when grown with canola or in pure stands.
• All pea varieties had larger seeds when grown with Cutlass than when grown with canola or in pure stands.
• Producers may benefit by intercropping peas with an oilseed rather than growing peas alone when oilseed prices are about 1 1/4 times the pea price.